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An examination of the sources of calcium for contractions mediated by postjunctional α 1 ‐ and α 2 ‐adrenoceptors in several blood vessels isolated from the rabbit
Author(s) -
Daly C.J.,
Dunn W.R.,
McGrath J.C.,
Miller D.J.,
Wilson V.G.
Publication year - 1990
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1990.tb14690.x
Subject(s) - rauwolscine , prazosin , saline , vasoconstriction , blood vessel , vein , anatomy , abdominal aorta , artery , calcium , medicine , aorta , chemistry , endocrinology , receptor , antagonist
1 The roles of intracellular and extracellular‐derived Ca 2+ in α‐adrenoceptor‐mediated contractions to noradrenaline (NA) have been investigated in several isolated blood vessels from the rabbit by examining responses in the presence of a modified Krebs‐Henseleit saline with 2.5 m m Ca 2+ and a Ca 2+ ‐buffered saline with 0.1 μ m free Ca 2+ . 2 NA was tested in preparations of the abdominal aorta, distal saphenous artery, renal vein, lateral saphenous vein, plantaris vein and ear vein exposed to a Ca 2+ ‐buffered saline with 0.1 μ m [Ca 2+ ]. A concentration of NA which was maximally effective in modified Krebs‐Henseleit saline, produced an initial transient contraction (ITC) followed by a relaxation towards baseline. This is evidence that α‐adrenoceptor‐mediated responses in all these blood vessels depend upon calcium from both sources. 3 The ITC was particularly pronounced in the arteries and was associated more closely with the α 1 ‐receptor subtype. In the abdominal aorta, distal saphenous artery and renal vein the ITC can almost exclusively be attributed to an α 1 ‐adrenoceptor (prazosin‐sensitive, rauwolscine‐resistant). In the ear vein, and to a lesser extent the plantaris vein, the ITC was mediated in part by an α 2 ‐adrenoceptor (prazosin‐resistant, rauwolscine‐sensitive). 4 α 2 ‐Adrenoceptors in the lateral saphenous vein largely account for the response to NA in modified Krebs‐Henseleit saline, but α 1 ‐adrenoceptors mediate the ITC in Ca 2+ ‐buffered saline. After selective inactivation of α 1 ‐adrenoceptors with a combination of phenoxybenzamine and rauwolscine, responses to NA in modified Krebs‐Henseleit saline are slow in onset and there is no ITC in Ca 2+ ‐buffered saline. 5 The possible significance of the coupling of postjunctional α 2 ‐adrenoceptors to dual sources of Ca 2+ is discussed in relation to the interaction between α‐adrenoceptor subtypes and the ease of demonstrating functional α 2 ‐adrenoceptors in isolated blood vessels.